KR20240004679A - Manufacturing method of grain-oriented electrical steel sheet - Google Patents

Abstract

The method for manufacturing a grain-oriented electrical steel sheet of the present invention includes, in mass%, C: 0.02 to 0.10%, Si: 2.5 to 5.5%, Mn: 0.01 to 0.30%, sol.Al: 0% or more but less than 0.010%, N: 0 A steel slab containing a total of 0% to less than 0.006% of S and Se, and a total of 0% to less than 0.010% of S and Se, with the remainder being Fe and inevitable impurities, is heated to a temperature of 1300°C or lower. After hot rolling, one cold rolling or two or more cold rollings with intermediate annealing in between are performed to obtain a cold rolled sheet of the final thickness, primary recrystallization annealing that also serves as decarburization annealing is performed, and an annealing separator is applied. A grain-oriented electrical steel sheet is manufactured by performing final annealing, and in the annealing process before cold rolling to the final sheet thickness described above, the steel sheet is cooled from 800°C to 400°C at an average cooling rate of 15°C/s or more after soaking, and then cooled at an average cooling rate of 15°C/s or more. Afterwards, low-temperature heat treatment is performed by keeping the product at a temperature between 60 and 100 degrees Celsius for 30 to 600 seconds.

Description

Manufacturing method of grain-oriented electrical steel sheet

The present invention relates to a method of manufacturing a so-called grain-oriented electrical steel sheet in which crystal grains are highly integrated with {110} on the sheet surface according to the Miller index and <001> in the rolling direction.

Grain-oriented electrical steel sheets use secondary recrystallization to highly integrate crystal grains in the {110}<001> orientation (hereinafter referred to as “Goss orientation”), thereby providing excellent magnetic properties with low iron loss and high magnetic flux density. Since it is a soft magnetic material with magnetic properties, it is mainly used as an iron core material for electrical devices such as transformers. Additionally, as an indicator of the magnetic properties of a grain-oriented electrical steel sheet, generally, the magnetic flux density B 8 (T) when the magnetic field strength is 800 (A/m) and the magnetic flux density B ₈ (T) in an alternating magnetic field with an excitation frequency of 50 (Hz) are 1.7. The iron loss per 1 kg of steel sheet when magnetized to (T) is W _17/50 (W/kg).

In the method for producing the grain-oriented electrical steel sheet described above, a fine precipitate called an inhibitor is deposited during the final annealing to provide a mobility difference to the grain boundaries, thereby providing Goss orientation grains (Goss orientation grains). A method of preferentially growing only grains is commonly used. For example, Patent Document 1 discloses a method using AlN and MnS as inhibitors, and Patent Document 2 discloses a method using MnS and MnSe as inhibitors, and both have been put to industrial use.

The ideal method of using these inhibitors is to have the inhibitors uniformly and finely dispersed, and therefore, it is necessary to heat the steel slab as a material to a high temperature of 1300°C or higher before hot rolling. Therefore, in the method of using the inhibitor described above, scale loss increases due to high-temperature heating, resulting in lower yield, increased heat energy cost and equipment cost, and complicated equipment maintenance, etc. there is a problem. Therefore, the demand for reduction in manufacturing costs has not been sufficiently met.

Meanwhile, as a technology to solve the above problems, a manufacturing method that does not use an inhibitor (inhibitorless method) has also been proposed. For example, in Patent Document 3 and the like, a technology using highly purified steel materials that do not contain inhibitor forming components is proposed. This technology excludes impurities such as inhibitor components as much as possible, making the grain boundary orientation angle dependence of the grain boundary energy during primary recrystallization visible, and Goss orientation grains are preferentially converted to secondary even without using an inhibitor. It is a recrystallization technology. Additionally, the above effect is called the “texture inhibition effect.” This method has many advantages in terms of manufacturing over the method using an inhibitor because high-temperature slab heating is unnecessary.

In addition, as a method of increasing the magnetic flux density by controlling the primary recrystallization texture, Patent Document 4 describes the method of controlling the temperature history of the steel sheet between coiling after annealing before final cold rolling and the start of cold rolling, thereby increasing the magnetic flux density of the edge portion of the steel sheet. A technology for preventing cracks and improving magnetic properties has been disclosed.

Japanese Patent Publication No. 40-015644 Japanese Patent Publication No. 51-013469 Japanese Patent Publication No. 2000-129356 Japanese Patent Publication No. 2003-253335

However, in the technology using a material that does not contain an inhibitor-forming component disclosed in Patent Document 3, etc., high-temperature slab heating is unnecessary, making it possible to manufacture a grain-oriented electrical steel sheet at low cost, while the inhibitor-forming component is not used. Although it does not contain it, it lacks the ability to suppress normal grain growth (primary recrystallization grain growth), so the orientation integration of the Goss grains that grow during secondary recrystallization is low, and the magnetic flux density of the product is lower than that of materials using inhibitors. tends to lag behind. Therefore, in order to manufacture products with high magnetic flux density, it becomes important to strictly control the texture of the primary recrystallized grains before secondary recrystallization. In addition, even if the technology of Patent Document 4 was applied to the above technology, the improvement in the magnetic flux density of the product plate was not sufficient.

The present invention was made in consideration of the above-mentioned problems faced by the prior art, and its purpose is to produce a grain-oriented electrical steel sheet with a high magnetic flux density inexpensively and stably using a steel material that does not contain inhibitor-forming components. The aim is to propose a manufacturing method.

The inventors have repeatedly studied methods for solving the above problems. As a result, in the annealing process performed immediately before cold rolling to the final sheet thickness (final cold rolling), rapid cooling is performed after cracking treatment, and then low-temperature heat treatment is performed to maintain the plate at a low temperature. Alternatively, by applying strain to the steel sheet immediately before or during the low-temperature heat treatment and appropriately managing the time from completion of the low-temperature heat treatment to the start of final cold rolling, the magnetic flux density of the product sheet can be increased compared to before. By discovering what was possible, we developed the present invention.

The present invention based on the above recognition contains C: 0.02 to 0.10 mass%, Si: 2.5 to 5.5 mass%, Mn: 0.01 to 0.30 mass%, and further, sol.Al: 0 mass% or more but less than 0.010 mass%, N: A steel slab containing 0 mass% or more but less than 0.006 mass%, a total of at least 0 mass% or more but less than 0.010 mass% of S and Se, and the remainder being Fe and inevitable impurities, at a temperature of 1300°C or lower. After heating to the desired temperature, hot rolling and annealing of the hot-rolled sheet, or, without annealing the hot-rolled sheet, one cold rolling or two or more cold rollings with intermediate annealing in between, to obtain a cold-rolled sheet of the final thickness. In the method of manufacturing a grain-oriented electrical steel sheet including the steps of performing primary recrystallization annealing that also serves as decarburization annealing, applying an annealing separator, and performing final annealing, in the annealing process immediately before cold rolling to the final sheet thickness, , After the cracking treatment, it is cooled from 800°C to 400°C at an average cooling rate of 15°C/s or more, and then subjected to low-temperature heat treatment by keeping it at a temperature between 60°C and 100°C for 30 to 600 s. A method for manufacturing grain-oriented electrical steel sheets is proposed.

The method of manufacturing the grain-oriented electrical steel sheet of the present invention includes, in the annealing process before cold rolling to the final sheet thickness, cooling from 800°C to 400°C at an average cooling rate of 15°C/s or more after soaking, and further , imparting strain to the steel sheet before performing low-temperature heat treatment held at a temperature between 60 and 100°C for 30 to 600 s, or during low-temperature heat treatment held at a temperature between 60 and 100°C for 30 to 600s. It is characterized by

In addition, the method of producing the grain-oriented electrical steel sheet of the present invention includes a method of imparting strain to the steel sheet, a method of performing at least one bending process by winding the steel sheet at an angle of 90° or more, and a method of performing rolling under light pressure. It is characterized by at least one of:

In addition, the method for manufacturing a grain-oriented electrical steel sheet of the present invention is characterized in that final cold rolling is started within 300 hr after completing the low-temperature heat treatment.

Additionally, the method for manufacturing a grain-oriented electrical steel sheet of the present invention is characterized by having a process that satisfies the following conditions.

energy

· The steel slab is heated, rough rolling is performed in a temperature range of 900 to 1,200°C in one pass or more, and then finish rolling is performed in a temperature range of 700 to 1,000°C in two or more passes to form a hot-rolled sheet, and then the steel slab is rolled in a temperature range of 400 to 750°C. Hot rolling process of winding into coils at a coiling temperature of ℃

When performing annealing of a hot-rolled sheet, a hot-rolled sheet annealing process is performed in which the sheet is kept in a temperature range of 800 to 1250°C for 5 seconds or more and then cooled from 800°C to 400°C at 5 to 100°C/s.

· When performing intermediate annealing, an intermediate annealing process is held in the temperature range of 800 to 1250°C for 5 seconds or more, and then cooled from 800°C to 400°C at 5 to 100°C/s.

·Cold rolling process in which the total reduction ratio of the final cold rolling is in the range of 80 to 92%.

· A primary recrystallization annealing process that also includes decarburization annealing, containing H ₂ and N ₂ and maintaining the decarburization annealing for more than 10 s in a temperature range of 750 to 950° C. in a humid atmosphere with a dew point of 20 to 80° C. or lower.

·Annealing separator application process in which an annealing separator containing MgO as a main ingredient is applied to the surface of the steel sheet in an amount of more than 2.5 g/m2 per side.

· A final annealing process in which a portion of the atmosphere in the temperature range of 800°C or higher is made into an H ₂ -containing atmosphere, including a purification treatment in which the temperature is kept at a temperature of at least 1,050 to 1,300°C for 3 hours or more.

In addition, the steel slab used in the method for producing the grain-oriented electrical steel sheet of the present invention further contains Ni: 0 to 1.00 mass%, Sb: 0 to 0.50 mass%, and Sn: 0 to 0.50 mass%. , Cu: 0 to 0.50 mass%, Cr: 0 to 0.50 mass%, P: 0 to 0.50 mass%, Mo: 0 to 0.50 mass%, Nb: 0 to 0.020 mass%, V: 0 to 0.010 mass%, B : 0 to 0.0025 mass%, Bi: 0 to 0.50 mass%, and Zr: 0 to 0.10 mass% or less.

In addition to the above component composition, the steel slab used in the method for producing the grain-oriented electrical steel sheet of the present invention further contains at least one selected from among Co: 0 to 0.0500 mass% and Pb: 0 to 0.0100 mass%. It is characterized by containing.

In addition, the steel slab used in the method for producing the grain-oriented electrical steel sheet of the present invention further contains As: 0 to 0.0200 mass%, Zn: 0 to 0.0200 mass%, and W: 0 to 0.0100 mass%. , Ge: 0 to 0.0050 mass% and Ga: 0 to 0.0050 mass%.

According to the method for manufacturing a grain-oriented electrical steel sheet of the present invention, it becomes possible to inexpensively and stably manufacture a grain-oriented electrical steel sheet having a high magnetic flux density.

Figure 1 is a diagram showing the effects of the cooling rate in the annealing process immediately before final cold rolling, low-temperature heat treatment conditions, and the time from low-temperature heat treatment to the start of final cold rolling on the magnetic flux density of the product plate.
Figure 2 is a diagram showing the effect of low-temperature heat treatment conditions and strain on the steel sheet on the magnetic flux density of the product sheet.

(Form for carrying out the invention)

First, the experiments that led to the development of the present invention will be described.

<Experiment 1>

Contains C: 0.03 mass%, Si: 3.2 mass%, Mn: 0.08 mass%, sol.Al: 0.005 mass%, N: 0.004 mass%, and S: 0.005 mass%, with the balance consisting of Fe and inevitable impurities. A steel slab having the following chemical composition was manufactured, the slab was heated to 1200°C, hot rolled to form a hot rolled sheet with a thickness of 2.5 mm, water cooled, and wound into a coil at 600°C. Subsequently, after cracking the hot-rolled sheet at 1000°C Then, hot-rolled sheet annealing was performed by cooling to 40°C or lower. Afterwards, low-temperature heat treatment is performed to remove scale from the surface of the steel sheet, heating it to each temperature of 40℃, 60℃, 80℃, 100℃, and 120℃, and maintaining it at each temperature for 0s, 30s, 300s, 600s, and 900s. After carrying out this, it was water-cooled and wound into a coil again. Thereafter, after completing the low-temperature heat treatment, cold rolling was started after 50 hr, 300 hr, and 500 hr had elapsed to obtain a cold-rolled sheet with a final sheet thickness (product thickness) of 0.27 mm.

Subsequently, the cold rolled _sheet was subjected to primary recrystallization annealing combined with decarburization annealing at ₈₂₀ °C It was applied at 3 g/m2 per side, dried, secondary recrystallized, and then subjected to final annealing to purify under the conditions of 1200°C x 5 hours. In addition, in the above-mentioned final annealing, the temperature range of 1100°C or higher was set in an atmosphere containing H ₂ as a main component. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film was applied, and flattening annealing was performed to both bake the film and flatten the steel sheet to obtain a product sheet. .

A test piece for measuring magnetic properties was taken from the product plate obtained in this way, and the magnetic flux density B ₈ at a magnetizing power of 800 A/m was measured by the method described in JIS C 2550-1 (2011), and the results are summarized in the figure. Shown in 1. From this figure, in order to obtain a good magnetic flux density of B ₈ ≥ 1.86T, the temperature from 800°C to 400°C in the cooling process after soaking treatment of hot-rolled sheet annealing is cooled at an average cooling rate of 15°C/s or more. It can be seen that after the cooling, it is necessary to perform low-temperature heat treatment by maintaining the product at a temperature of 60 to 100°C for 30 to 600 seconds. In addition, it can be seen that a better magnetic flux density of B ₈ ≥ 1.87T can be obtained by starting the final cold rolling within 300 hr after completing the above low-temperature heat treatment.

As described above, the average cooling rate from 800°C to 400°C in the cooling process of hot-rolled sheet annealing is set to 15°C/s or more, and then maintained at a temperature between 60°C and 100°C for 30 to 600 s at a low temperature. The reason why the magnetic flux density of the product plate is improved by performing heat treatment or, additionally, by starting final cold rolling within 300 hours after completing the low-temperature heat treatment is not yet sufficiently clear at present, but the inventors are as follows: We are thinking together.

First, after cracking the hot-rolled sheet by annealing, it is rapidly cooled in the temperature range of 800°C to 400°C, so that the C dissolved in the steel does not precipitate as carbide and remains in a solid-solution state. Additionally, with rapid cooling, many lattice defects such as dislocations and vacancies are introduced into the steel sheet. When low-temperature heat treatment is performed in this state, solid solution C is fixed to lattice defects, and precipitation of carbides is suppressed. However, if the temperature of the low-temperature heat treatment is too low or the retention time is too short, the fixation effect cannot be sufficiently obtained. On the other hand, if the temperature of the low-temperature heat treatment is too high or the retention time is too long, carbide It becomes precipitated.

However, it is thought that in the steel sheet after the low-temperature heat treatment, there still remains solid solution C that is not fixed to lattice defects and can move freely. Therefore, by limiting the time until the start of the final cold rolling and performing cold rolling before the solid solution C precipitates as carbide, the solid solution C can remain even in the steel sheet after the final cold rolling. As also described in Patent Document 4, materials containing a large amount of dissolved C are thought to have the effect of improving the primary recrystallization texture formed in the subsequent cold rolling and decarburization annealing, and as a result, among the primary recrystallization grains , it is thought that only particles with an ideal Goss orientation can grow into secondary recrystallized grains during final annealing, which increases the magnetic flux density of the product plate.

<Experiment 2>

Contains C: 0.06 mass%, Si: 3.5 mass%, Mn: 0.10 mass%, sol.Al: 0.003 mass%, N: 0.002 mass%, and S: 0.008 mass%, with the balance consisting of Fe and inevitable impurities. A steel slab having the following chemical composition was manufactured, the slab was heated to 1280°C, hot rolled to form a hot rolled sheet with a thickness of 2.8 mm, and then water cooled and wound into a coil at 600°C. Next, after removing the scale on the surface of the steel sheet, a first cold rolling was performed to make the intermediate sheet thickness 1.5 mm, followed by cracking at 1050°C and continued to cool to 40°C or lower. After removing the scale on the surface of the steel sheet, some of the coils were subjected to bending processing once by winding them at angles of 60°, 90°, and 180° on a roll with a diameter of 1000 mmϕ at a rolling speed of 30 m/min. , low-temperature heat treatment was performed at temperatures of 50°C, 70°C, 90°C, and 110°C for 20s, 200s, 400s, 600s, and 800s, followed by water cooling and coiling again. Thereafter, 50 hours after completion of the low-temperature heat treatment, a second cold rolling (final cold rolling) was performed to obtain a cold-rolled sheet with a final thickness of 0.27 mm.

Subsequently, _primary recrystallization annealing combined with _{decarburization} annealing at 880°C It was applied and dried at a rate of /m2, then secondary recrystallization was performed, and then final annealing was performed to purify it at 1180°C x 20 hr. In addition, in the above-mentioned final annealing, the temperature range of 900°C or higher was set in an atmosphere containing H ₂ as a main component. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film was applied, and a flattening annealing was performed that also flattened the coating and the steel strip to obtain a product plate. .

A test piece for measuring magnetic properties was taken from the product plate obtained in this way, and the magnetic flux density B ₈ at a magnetizing power of 800 A/m was measured by the method described in JIS C 2550-1 (2011), and the results are summarized in the figure. Shown in 2. From this figure, in the annealing process immediately before final cold rolling, low-temperature heat treatment is performed by cooling from 800°C to 400°C at an average cooling rate of 15°C/s or more and then maintaining the temperature at a temperature between 60°C and 100°C for 30 to 600 s. It can be seen that an excellent magnetic flux density of B ₈ ≧1.89T is obtained by performing bending processing by winding the steel sheet on a roll at an angle of 90° or more and applying strain to the steel sheet before performing the process.

As described above, in the annealing process before final cold rolling, low-temperature heat treatment is performed by cooling from 800°C to 400°C at an average cooling rate of 15°C/s or more and maintaining the heat treatment at a temperature between 60°C and 100°C for 30 to 600 s. The reason why the magnetic flux density of the product sheet is further improved by bending the steel sheet at an angle of 90° or more and applying strain to the steel sheet before implementation is not fully clear at this time, but the inventors are as follows: We are thinking together.

It is believed that the quenching effect in intermediate annealing and the effect of subsequent low-temperature heat treatment are the same as described in <Experiment 1>. However, by applying strain to the steel sheet by performing bending processing by winding it around a roll at an angle of 90° or more, It is thought that as a result of the increase in the density of lattice defects and the increase in the amount of solid solution C fixed to the lattice defects during the subsequent low-temperature heat treatment, the primary recrystallization texture was improved and the magnetic flux density of the product plate was further increased.

Next, the chemical composition that the steel material (slab) used for manufacturing the grain-oriented electrical steel sheet of the present invention must have is explained.

C: 0.02 to 0.10 mass%

C is a component necessary to improve the structure of the hot-rolled sheet by utilizing the austenite-ferrite transformation that occurs during hot rolling and cracking during annealing of the hot-rolled sheet. In addition, if the C content does not meet 0.02 mass%, the grain boundary strengthening effect due to C is lost, which may cause problems in manufacturing, such as cracks forming in the slab. On the other hand, if the C content exceeds 0.10 mass%, not only does the load of the decarburization annealing process increase, but the decarburization itself becomes incomplete, causing magnetic aging of the product plate. Therefore, the C content is set to be in the range of 0.02 to 0.10 mass%. Preferably it is in the range of 0.03 to 0.08 mass%.

Si: 2.5 to 5.5 mass%

Si is a very effective component in increasing the specific resistance of steel and reducing eddy current loss, which constitutes a part of iron loss. However, if the Si content is less than 2.5 mass%, the specific resistance is low and good iron loss characteristics cannot be obtained. On the other hand, the specific resistance of steel increases monotonically up to 11 mass% of Si content, but when it exceeds 5.5 mass%, workability decreases significantly and rolling becomes difficult. Therefore, the Si content is set to be in the range of 2.5 to 5.5 mass%. Preferably it is in the range of 3.0 to 4.0 mass%.

Mn: 0.01∼0.30mass%

Mn is an effective ingredient for improving hot workability. However, if it is less than 0.01 mass%, the above effect cannot be sufficiently obtained, and if it exceeds 0.30 mass%, the magnetic flux density of the product plate decreases, so the Mn content is set in the range of 0.01 to 0.30 mass%. Preferably it is in the range of 0.05 to 0.20 mass%.

sol.Al: 0mass% or more but less than 0.010mass%, N: 0mass% or more but less than 0.006mass%, at least one of S and Se: 0mass% or more and less than 0.010mass% in total

Since the present invention is a technology for secondary recrystallization of the Goss orientation through the texture inhibition effect without using an inhibitor to cause secondary recrystallization, Al, N, S, and Se, which are inhibitor forming components, It is necessary to reduce the content as much as possible. For this reason, it is necessary to use a steel material in which Al is reduced to less than 0.010 mass% as sol.Al (acid-soluble Al), N: less than 0.0060 mass%, and at least one of S and Se reduced to less than 0.010 mass% in total. . Preferably, sol.Al: 0 to 0.008 mass%, N: 0 to 0.0050 mass%, and at least one of S and Se in the total range of 0 to 0.007 mass%. However, since reduction of these components causes an increase in manufacturing costs, it is not necessarily necessary to reduce them to 0 mass%.

In addition to the above basic components, the steel material used in the present invention further contains Ni: 0 to 1.00 mass%, Sb: 0 to 0.50 mass%, Sn: 0 to 0.50 mass%, and Cu for the purpose of improving magnetic properties. : 0 to 0.50 mass%, Cr: 0 to 0.50 mass%, P: 0 to 0.50 mass%, Mo: 0 to 0.50 mass%, Nb: 0 to 0.020 mass%, V: 0 to 0.010 mass%, B: 0 It may contain at least one selected from the group consisting of ∼0.0025 mass%, Bi: 0 to 0.50 mass%, and Zr: 0 to 0.10 mass%. If the content of each component exceeds the above upper limit, the development of secondary recrystallized grains is suppressed, and there is a risk that the magnetic properties may deteriorate. In addition, from the viewpoint of further improving magnetic properties, Ni: 0.01 mass% or more, Sb: 0.005 mass% or more, Sn: 0.005 mass% or more, Cu: 0.01 mass% or more, Cr: 0.01 mass% or more, P: 0.005 mass% or more % or more, Mo: 0.005 mass% or more, Nb: 0.001 mass% or more, V: 0.001 mass% or more, B: 0.0002 mass% or more, Bi: 0.005 mass% or more, and Zr: 0.001 mass% or more.

In addition to the above component composition, the steel material used in the present invention contains at least one selected from Co: 0 to 0.0500 mass% and Pb: 0 to 0.0100 mass% for the purpose of improving magnetic properties. It may contain. If the content of each component exceeds the above upper limit, the development of secondary recrystallized grains is suppressed, and the magnetic properties actually deteriorate. Additionally, from the viewpoint of further improving magnetic properties, it is preferable to contain Co: 0.0020 mass% or more and Pb: 0.0001 mass% or more.

In addition to the above composition, the steel material used in the present invention contains As: 0 to 0.0200 mass%, Zn: 0 to 0.0200 mass%, and W: 0 to 0.0100 mass% for the purpose of improving magnetic properties. , Ge: 0 to 0.0050 mass%, and Ga: 0 to 0.0050 mass%. If the content of each component exceeds the above upper limit, the development of secondary recrystallized grains is suppressed, and the magnetic properties actually deteriorate. Additionally, from the viewpoint of further improving magnetic properties, it is preferable to contain As: 0.0010 mass% or more, Zn: 0.0010 mass% or more, W: 0.0010 mass% or more, Ge: 0.0001 mass% or more, and Ga: 0.0001 mass% or more. .

In the steel material used in the present invention, the remainder other than the above-mentioned components is Fe and inevitable impurities. Here, the above-mentioned inevitable impurities mean those that are inevitably mixed in from raw materials, scrap, ladle in the solvent, external environment, etc. when melting a slab. Additionally, Ti, which is contained as an inevitable impurity, is a harmful component that forms nitride and inhibits secondary recrystallization of Goss grains. However, excessive reduction results in an increase in refining costs, but can be tolerated if it is 0.010 mass% or less. Preferably it is 0.0020 mass% or less.

Next, the manufacturing method of the grain-oriented electrical steel sheet of the present invention will be described.

The slab used as the steel material for the grain-oriented electrical steel sheet of the present invention is preferably manufactured by melting steel having the above-mentioned chemical composition through a commonly known refining process and then using a generally known ingot method or continuous casting method. Additionally, thin cast pieces with a thickness of 100 mm or less may be manufactured by direct casting.

The steel material (slab or thin cast piece) obtained as described above is heated to a predetermined temperature by a normal method and then subjected to hot rolling. However, it may be hot rolled immediately after casting without heating. In addition, the slab heating temperature before hot rolling is preferably set to 1300°C or lower from the viewpoint of cost reduction because the slab does not contain inhibitor forming components.

In the subsequent hot rolling, it is preferable from the viewpoint of controlling the structure of the hot rolled sheet that one or more passes of rough rolling are performed in a temperature range of 900 to 1,200°C, followed by two or more passes of finish rolling in a temperature range of 700 to 1,000°C. Additionally, the coil winding temperature after hot rolling is preferably in the range of 400 to 750°C from the viewpoint of preventing defects such as cracks. A more preferable coiling temperature is in the range of 500 to 700°C.

The steel sheet after the above hot rolling may then be subjected to hot rolled sheet annealing as needed. By annealing the hot-rolled sheet, uniformity of the structure can be achieved and variation in magnetic properties can be reduced. When annealing a hot-rolled sheet, from the viewpoint of uniformizing the structure, it is preferable to perform soaking treatment at a temperature of 800 to 1,250°C for 5 seconds or more. More preferably, the storage condition is maintained at a temperature of 900 to 1,150°C for 10 to 180 seconds. In addition, for cooling after the soaking treatment, it is preferable that the cooling rate from 800°C to 400°C be in the range of 5 to 100°C/s from the viewpoint of controlling the shape of the second phase and precipitates. A more preferable cooling rate is in the range of 15 to 80° C./s.

Next, in order to remove scale from the surface of the steel sheet created during hot rolling, it is preferable to descale it using a method such as pickling using heated acid or a method of mechanically removing scale.

Next, the descaled hot-rolled sheet is subjected to one cold rolling, or two or more cold rollings with intermediate annealing in between, to obtain a cold-rolled sheet of the final sheet thickness (product sheet thickness). When performing intermediate annealing, from the viewpoint of structure control, it is preferable to perform soaking treatment in a temperature range of 800 to 1250°C for 5 seconds or more. In addition, from the viewpoint of controlling the shape of the second phase and precipitates, the cooling rate after the soaking treatment is preferably set to a cooling rate of 5 to 100°C/s from 800°C to 400°C. A more preferable cooling rate is in the range of 15 to 80° C./s. In addition, when performing intermediate annealing, it is preferable to wash beforehand to remove the rolling oil from the previous process. In addition, after intermediate annealing, it is preferable to remove the scale formed on the surface of the steel sheet by the method described above. In addition, in the present invention, cold rolling to the final sheet thickness is referred to as “final cold rolling.”

Here, the most important thing in the present invention is that in the annealing process immediately before final cold rolling, in the cooling process after soaking, cooling is performed from 800°C to 400°C at an average cooling rate of 15°C/s or more, and thereafter, 60°C Low-temperature heat treatment is performed by preserving the product at a temperature between ∼100°C for 30∼600 seconds. Here, the annealing process immediately before the final cold rolling refers to hot-rolled sheet annealing in the case of cold rolling to the final sheet thickness (product sheet thickness) with one cold rolling, and in the case of performing two or more cold rollings with intermediate annealing in between. refers to intermediate annealing immediately before final cold rolling. Therefore, when the hot-rolled sheet annealing process or intermediate annealing process described above corresponds to the annealing process immediately before final cold rolling, the cooling conditions described above (cooling rate from 800°C to 400°C: 5 to 100°C/s) ) needs to be suitable for the above cooling conditions (average cooling rate of 15°C/s or more from 800°C to 400°C).

In addition, the low-temperature heat treatment process of maintaining the temperature for 30 to 600 seconds at a temperature between 60 and 100°C, which follows the annealing process, may be performed continuously on the same annealing line, or may be performed once by cooling to 100°C or lower and winding it into a coil. After doing this, you can do it on another line. Preferred low-temperature heat treatment conditions are conditions in which the product is maintained at a temperature between 70 and 90° C. for 60 to 300 seconds. Additionally, the low-temperature heat treatment may be performed concurrently with (simultaneously) other treatments such as acid washing, as long as the storage temperature and storage time are within the above ranges.

Additionally, the next important thing in the present invention is to impart strain to the steel sheet immediately before or during the low-temperature heat treatment. As a method for imparting strain, general methods such as a method of performing bending by winding on a roll or a method of performing hard cold rolling can be used. When using bending processing, it is desirable to wind the roll at an angle of 90° or more with a diameter of 200 to 2500 mmϕ and perform bending processing at least once, more preferably 2 to 10 times. As the roll, a dedicated roll for imparting deformation may be used, but a deflector roll or pinch roll installed in the production line may be used instead. Additionally, the imparting of the strain may be performed within an annealing line or an acid cleaning line, or may be performed on another production line for the purpose of imparting the strain. On the other hand, when performing light pressure rolling, for example, in a skin pass roll, it is preferable to perform light pressure rolling at a reduction ratio of 0.5 to 10%, more preferably 1 to 5%. .

Additionally, another important thing in the present invention is to start the final cold rolling within 300 hr after completing the low-temperature heat treatment. If the temperature exceeds 300 hr, the amount of solid solution C remaining in the steel sheet decreases, the primary recrystallization texture deteriorates, resulting in deterioration of the magnetic properties of the product sheet. More preferably, it is 100 hr or less.

In addition, the total reduction ratio of the final cold rolling is preferably in the range of 80 to 92% from the viewpoint of obtaining a good primary recrystallization texture before secondary recrystallization. Additionally, from the viewpoint of improving the magnetic properties by improving the recrystallization texture, warm rolling is performed by raising the temperature of the steel sheet during cold rolling to 100 to 300 ° C, or aging at a temperature of 100 to 300 ° C during cold rolling. It is preferable to perform the treatment once or multiple times. In addition, in the cold rolling described above, it is preferable to use a lubricant such as rolling oil from the viewpoint of reducing the rolling load and controlling the rolled shape.

The cold-rolled sheet of the final thickness is degreased or pickled as necessary, and the surface of the steel sheet is cleaned, and then subjected to primary recrystallization annealing that also serves as decarburization annealing. Decarburization annealing is preferably maintained for 10 seconds or more in a temperature range of 750 to 950°C. In addition, it is preferable that the atmosphere during decarburization annealing is a wet atmosphere containing H ₂ and N ₂ and having a dew point of 20 to 80°C in part or all of the range of decarburization annealing. More preferably, the conditions are such that the dew point is maintained for 30 to 180 seconds in a temperature range of 800 to 900°C in a humid atmosphere of 40 to 70°C. By performing the decarburization annealing, C in the steel is reduced to 0.0050 mass% or less, where self-aging is difficult to occur.

For the steel sheet after the decarburization annealing, it is preferable to apply an annealing separator mainly composed of MgO to the surface of the steel sheet in an amount of 2.5 g/m 2 or more per side. MgO may be applied to a steel plate in the form of a slurry, or may be applied dry by electrostatic coating. When applying as a slurry, it is preferable to maintain the slurry solution at a temperature of 15°C or lower in order to suppress an increase in viscosity. In addition, in order to keep the slurry concentration constant, it is desirable to manage the slurry solution by dividing it into a tank for preparation and a tank for the solution used for application. Here, the fact that the annealing separator is mainly composed of MgO means that the content of MgO in the annealing separator is 60 mass% or more.

The steel sheet to which the annealing separator has been applied is subjected to final annealing while wound into a coil, thereby developing secondary recrystallized grains and forming a forsterite film on the surface of the steel sheet. At this time, in order to complete secondary recrystallization, it is preferable to heat to a temperature of 800°C or higher, and in order to form a forsterite film, it is preferable to heat to a temperature of 1050°C or higher. In addition, in order to exclude impurities such as inhibitor-forming components from the steel and obtain good magnetic properties, purification treatment is performed by maintaining the steel for more than 3 hours in the temperature range of 1050 to 1300°C, and some or all of the steel is stored at a temperature range of 800°C or higher. It is preferable that the temperature range is an atmosphere containing H ₂ . By performing the above purification treatment, the inhibitor forming component can be reduced to the impurity level. In addition, since final annealing involves heat treatment at a high temperature for a long period of time, it is common to anneal the coil in the up-end state. However, in order to prevent the winding outside the coil from loosening, a band is placed around the coil before final annealing. It is advisable to wrap your back.

After the steel sheet has been subjected to the final annealing, the unreacted annealing separator remaining on the surface of the steel sheet is removed by water washing, brushing, pickling, etc., and then the steel sheet is subjected to flattening to correct winding properties or shape defects that occurred during the final annealing. Annealing is also desirable for reducing iron loss.

In addition, electrical steel sheets are often used by laminating steel sheets, but in order to ensure insulation, it is desirable to form an insulating film on the surface of the steel sheets. In order to reduce core loss, it is preferable to apply a tension-imparting type film that applies tension to the steel sheet as the insulating film. The formation of this insulating film may be performed by applying a coating solution before flattening annealing and baking it by flattening annealing, or may be performed on another line. In addition, if a method of forming a tension imparting film through a binder or depositing an inorganic film on the surface layer of the steel sheet using a physical vapor deposition method or a chemical vapor deposition method is adopted, a film having excellent adhesion and a significant iron loss reduction effect can be obtained. obtained.

Additionally, from the viewpoint of further reducing iron loss, in a certain process after cold rolling, a groove is formed on the surface of the steel sheet by etching, etc., or an insulating film is formed, and then a thermal energy beam such as a laser or plasma is irradiated to the surface of the steel sheet. Magnetic domain refining treatment may be performed by forming a heat deformation area or by pressing a roll having protrusions, etc. on the surface of the steel sheet to form a processing deformation area.

Example 1

Contains C: 0.03 mass%, Si: 3.1 mass%, Mn: 0.14 mass%, sol.Al: 0.008 mass%, N: 0.004 mass%, and S: 0.002 mass%, with the balance consisting of Fe and inevitable impurities. A steel slab having the same chemical composition was manufactured, heated to a temperature of 1250°C, hot rolled to form a hot rolled sheet with a thickness of 2.5 mm, and wound into a coil at a temperature of 600°C. Next, hot-rolled sheet annealing was performed on the hot-rolled sheet by soaking at 950°C Subsequently, after removing the scale on the surface of the steel sheet, a first cold rolling was performed to make the intermediate sheet thickness 1.8 mm, and after cracking at 1050°C x 30 s, the average cooling rate from 800°C to 400°C was 10°C/s. , water cooling was performed at three levels of 35°C/s and 80°C/s, and then intermediate annealing was performed by cooling to 40°C or lower.

Afterwards, low-temperature heat treatment was performed while acid washing and preservation at a temperature of 80°C for 200 seconds, followed by water cooling and winding again into a coil. At this time, strain was applied to the steel sheet under the conditions A to E shown in Table 1. Specifically, condition A is a condition in which no strain is applied, and condition B is bending processing by winding a roll with a diameter of 1000 mm ϕ at an angle of 90° at a sheet speed of 50 m/min after the intermediate annealing and before low temperature heat treatment. Condition C is a condition in which the bending process is performed three times at an angle of 180° on a roll with a diameter of 2000 mm ϕ at a sheet speed of 50 m/min after the intermediate annealing and before the low-temperature heat treatment. D is the condition of performing light pressure rolling with a reduction ratio of 2% once with a skin pass rolling mill having a work roll with a diameter of 1000 mm ϕ at a sheet speed of 50 m/min, condition E, after the intermediate annealing and before low temperature heat treatment. is a condition in which bending processing is performed once by winding a roll with a diameter of 1000 mmϕ at an angle of 90° at a sheet speed of 50 m/min during the low temperature heat treatment (after holding for 100 s).

Then, 200 hours after the low-temperature heat treatment, the steel sheet was subjected to a second cold rolling (final cold rolling) to obtain a cold rolled sheet with a final thickness of 0.18 mm. Subsequently, the cold _- rolled sheet was subjected to primary recrystallization annealing combined with decarburization annealing at ₈₀₀ °C It was applied at 5 g/m2 per side, dried, secondary recrystallized, and then subjected to final annealing to purify at 1160°C x 5 hr. In addition, in the above-mentioned final annealing, the temperature range of 1100°C or higher was set in an atmosphere containing H ₂ as a main component. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film was applied, and flattening annealing was performed to both bake the film and flatten the steel sheet to obtain a product sheet. .

A test piece for measuring magnetic properties was taken from the product plate obtained in this way, and the magnetic flux density B ₈ at a magnetizing power of 800 A/m was measured by the method described in JIS C2 550-1 (2011), and the results are shown in Table 1. It was done side by side. From these results, it can be seen that all steel sheets manufactured under conditions suitable for the present invention have good magnetic flux densities of B ₈ ≥ 1.87T. In particular, for steel sheets in which the intermediate annealing cooling rate was set to 80°C/s, a better magnetic flux density of B ₈ ≥ 1.89T was obtained.

(Table 1)

Example 2

A steel slab containing various components shown in Table 2 and having a composition of which the balance consists of Fe and inevitable impurities was manufactured, heated to a temperature of 1250°C, and then hot rolled to form a hot rolled sheet with a thickness of 2.0 mm. Then, it was water-cooled and wound into a coil at a temperature of 500°C. Next, hot-rolled sheet annealing was performed on each hot-rolled sheet by soaking at 1050°C x 30s, followed by water-cooling from 800°C to 400°C at an average cooling rate of 50°C/s, and then cooling to 40°C or lower. Next, while acid washing, low-temperature heat treatment was performed by maintaining the product at a temperature of 90°C for 60 seconds, followed by water cooling and coiling. At this time, after the hot-rolled sheet annealing and before the low-temperature heat treatment, bending processing was performed three times by winding a roll with a diameter of 1000 mmϕ at an angle of 90° at a sheet speed of 80 m/min.

Next, 20 hours after performing the low-temperature heat treatment, a second cold rolling (final cold rolling) was performed to obtain a cold rolled sheet with a final thickness of 0.23 mm. Next, _primary recrystallization annealing combined with _{decarburization} annealing at 840°C It was applied ㎡ and dried. After that, after secondary recrystallization, final annealing to purify at 1200°C x 20 hr was performed. In addition, in the above-mentioned final annealing, the temperature range of 1000°C or higher was set in an atmosphere containing H ₂ as a main component. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the final annealing, a phosphate-based tension-imparting insulating film was applied, and flattening annealing was performed to both bake the film and flatten the steel sheet to obtain a product sheet. .

A test piece for measuring magnetic properties was taken from the product plate obtained in this way, and the magnetic flux density B ₈ at a magnetizing power of 800 A/m was measured by the method described in JIS C 2550-1 (2011), and the results are shown in Table 2. It was done side by side. From these results, it can be seen that all steel sheets manufactured under conditions suitable for the present invention using steel materials (slabs) having a component composition suitable for the present invention have good magnetic flux densities of B ₈ ≥ 1.89T. In particular, all steel sheets to which arbitrary additive components were added in appropriate amounts achieved excellent magnetic flux densities of B ₈ ≥ 1.91T.

(Table 2-1)

(Table 2-2)

Claims (8)

C: 0.02 to 0.10 mass%, Si: 2.5 to 5.5 mass%, Mn: 0.01 to 0.30 mass%, and additionally, sol.Al: 0 mass% or more but less than 0.010 mass%, N: 0 mass% or more but less than 0.006 mass% , A steel slab containing at least 0 mass% and less than 0.010 mass% of at least one of S and Se in total, and the balance being Fe and inevitable impurities, is heated to a temperature of 1300°C or lower, and then hot rolled. After annealing the hot-rolled sheet, or without annealing the hot-rolled sheet, one cold rolling or two or more cold rollings with intermediate annealing in between are performed to obtain a cold-rolled sheet of the final thickness, followed by primary recrystallization combined with decarburization annealing. A method of manufacturing a grain-oriented electrical steel sheet including the steps of annealing, applying an annealing separator, and performing final annealing,
In the annealing process immediately before cold rolling to the final plate thickness, after soaking, cooling is performed from 800°C to 400°C at an average cooling rate of 15°C/s or more, and then at a temperature between 60°C and 100°C for 30 to 600 s. A method of manufacturing a grain-oriented electrical steel sheet, characterized by performing low-temperature heat treatment to maintain the shelf life. According to paragraph 1,
In the annealing process before cold rolling to the final plate thickness, after soaking, cooling is performed from 800°C to 400°C at an average cooling rate of 15°C/s or more, and then at a temperature between 60°C and 100°C for 30 to 600 s. A method of manufacturing a grain-oriented electrical steel sheet, characterized in that strain is applied to the steel sheet before performing low-temperature heat treatment to maintain its preservation, or during low-temperature heat treatment to maintain the temperature between 60 and 100° C. for 30 to 600 s. According to paragraph 2,
A method of producing a grain-oriented electrical steel sheet, wherein the method of imparting strain to the steel sheet is at least one of a method of performing bending processing at least once by winding the steel sheet at an angle of 90° or more and a method of performing rolling under light pressure. . According to any one of claims 1 to 3,
A method of manufacturing a grain-oriented electrical steel sheet, characterized in that the final cold rolling is started within 300 hours after completing the low-temperature heat treatment. According to any one of claims 1 to 4,
A method of manufacturing a grain-oriented electrical steel sheet, characterized by having a process that satisfies the following conditions.
energy
· The steel slab is heated, rough rolling is performed in a temperature range of 900 to 1,200°C in one pass or more, and then finish rolling is performed in a temperature range of 700 to 1,000°C in two or more passes to form a hot-rolled sheet, and then the steel slab is rolled in a temperature range of 400 to 750°C. Hot rolling process of winding into coils at a coiling temperature of ℃
When performing annealing of a hot-rolled sheet, a hot-rolled sheet annealing process is performed in which the sheet is kept in a temperature range of 800 to 1250°C for 5 seconds or more and then cooled from 800°C to 400°C at 5 to 100°C/s.
· When performing intermediate annealing, an intermediate annealing process is held in the temperature range of 800 to 1250°C for 5 seconds or more, and then cooled from 800°C to 400°C at 5 to 100°C/s.
·Cold rolling process in which the total reduction ratio of the final cold rolling is in the range of 80 to 92%.
· A primary recrystallization annealing process that also serves as decarburization annealing, containing H ₂ and N ₂ and maintaining the storage for 10 s or more in a temperature range of 750 to 950° C. in a humid atmosphere with a dew point of 20 to 80° C. or lower.
·Annealing separator application process in which an annealing separator containing MgO as a main ingredient is applied to the surface of the steel sheet in an amount of more than 2.5 g/m2 per side.
· A final annealing process in which a portion of the atmosphere in the temperature range of 800°C or higher is made into an H ₂ -containing atmosphere, including a purification treatment in which the temperature is kept at a temperature of at least 1,050 to 1,300°C for 3 hours or more. According to any one of claims 1 to 5,
In addition to the above component composition, the steel slab further contains Ni: 0 to 1.00 mass%, Sb: 0 to 0.50 mass%, Sn: 0 to 0.50 mass%, Cu: 0 to 0.50 mass%, Cr: 0 to 0.50. mass%, P: 0 to 0.50 mass%, Mo: 0 to 0.50 mass%, Nb: 0 to 0.020 mass%, V: 0 to 0.010 mass%, B: 0 to 0.0025 mass%, Bi: 0 to 0.50 mass% and Zr: 0 to 0.10 mass% or less. According to any one of claims 1 to 6,
A method for manufacturing a grain-oriented electrical steel sheet, wherein the steel slab further contains at least one selected from among Co: 0 to 0.0500 mass% and Pb: 0 to 0.0100 mass% in addition to the above component composition. According to any one of claims 1 to 7,
In addition to the above composition, the steel slab further contains As: 0 to 0.0200 mass%, Zn: 0 to 0.0200 mass%, W: 0 to 0.0100 mass%, Ge: 0 to 0.0050 mass%, and Ga: 0 to 0.0050 mass%. A method for manufacturing a grain-oriented electrical steel sheet, comprising at least one selected from mass%.